There are a variety of wheel slip control systems whose construction and operation are known in the rail transport industry. The objective of such systems is to vary the force that the brakes apply to the wheels of the rail vehicle during braking so that the wheels neither slide nor lockup as they travel on the top surface of the railway track. By adjusting the force with which the brakes apply so as to prevent or at least reduce slipping, a brake control system can more safely and efficiently decelerate and stop a rail vehicle in a shorter distance than would be possible without the use of a wheel slip control system.
Wheel slip control systems essentially control the interaction between the wheels and the tracks on which they ride. The top surface of the rails on which the tread of the wheels ride is typically called the running surface. The wheel treads adhere to the running surface of the rails essentially by means of friction. Under any given set of operating conditions, there exists between a wheel tread and the running surface on which it rides a particular level of frictional adhesion. It is this friction between tread and running surface which allows the wheel treads to have traction on the rails as the vehicle travels along the tracks. Should the braking force applied to the wheels exceed that which can be sustained by the maximum amount of frictional adhesion inherent to the particular wheel tread-running surface environment at issue, the treads will no longer completely grip and thus slip, and maybe even slide, on the running surface. It is such slipping and sliding that wheel slip control systems attempt to eliminate or at least reduce.
The typical wheel slip control system in the art today employs one or more microprocessors accompanied by a requisite number of memory storage devices, and may be embodied within the brake control system. These memory devices may, of course, be either separate from or actually embodied in the microprocessor(s) (hereinafter "microprocessor"). The microprocessor executes a specific set of instructions contained in programming code. The programming code, according to whose directions or logic the wheel slip control system operates, is stored in these memory devices. The microprocessor and associated memory devices are typically housed within a single package referred to as the wheel slip controller. It is this controller that controls various other parts of the wheel slip control system as explained hereinafter.
The memory storage devices may also be used to store numerous tables of parameters or a number of individual parameters or both. These parameters are constants, with variable values, each of which preselected to work in connection with the circumstances of its application. In other words, these parameters, whether individually or as part of a table, are generally "setup" or "tuned" to each individual application. As the microprocessor executes the instructions contained in the programming code, the programming code generally requires the microprocessor to retrieve one or more of the parameter values from memory to complete a particular task. Exactly which value in a parameter table the microprocessor retrieves depends on the conditions under which the vehicle is then operating. The parameters along with the programming code are required by the microprocessor to operate the system. The parameter values serve as referents for determining other variables in the process through which to control slipping of the wheels.
As is known in the rail transport industry, a passenger transit rail vehicle may feature friction braking equipment only or a combination of friction and dynamic braking equipment. The total braking effort sought to be applied by its brake control system is generally communicated via a brake command signal to the brake control equipment on the vehicle. A typical wheel slip control system basically affects how the brake control system formulates the brake command signal so that the signal accommodates whatever amount of reduction is necessary to resolve the slipping problem.
Passenger transit vehicles typically have two axles per truck. Regarding those vehicles that feature only friction braking, the two axles on the truck typically have friction brake control equipment in common. The friction braking effort sought to be applied is communicated via the brake command signal or its progeny to the modulation valve(s) of the friction brake control equipment. One modulation valve is typically connected to the brake cylinder(s) or brake cylinder supply line(s) on each truck or even each axle depending on how the vehicle is configured. The modulation valve can be manipulated to vary the friction braking force applied to the wheel/axle combination(s). The modulation valve can generally be commanded to assume any one of several positions. When commanded to a release position, for example, the valve vents pressure from the brake cylinders so as to release the brakes. When commanded to lap position, the valve holds constant whatever pressure is currently in the brake cylinders. When commanded to an apply position, the modulation valve supplies pressure to the brake cylinders so as to reapply the brakes.
Regarding those passenger transit vehicles that feature both friction and dynamic braking, each axle on a truck also typically has its own AC motor through which it may be propelled and dynamically braked. The dynamic braking effort sought to be applied is communicated to a propulsion brake controller of the dynamic braking equipment. The propulsion brake controller can be manipulated to vary the dynamic braking force that the AC motors apply to the axles. The propulsion brake controller typically has per truck control over the two AC motors on its truck.
Wheel slip control systems ideally prevent or at least reduce slipping by detecting nascent slipping and then correcting accordingly the force applied by the brakes to the wheels of the rail vehicle. Simply described, after the wheel slip is detected, the wheel slip control system corrects (i.e., temporarily reduces) the braking force applied to the slipping wheel until the rotational speed of the wheel and its associated axle again matches the speed of the rail vehicle. Once the rotational speed of the wheel/axle combination matches or perhaps briefly exceeds the speed of the rail vehicle, the wheel slip control system reapplies the braking force to the wheel. This process of detecting and correcting wheel slip occurs rapidly and generally continuously on most all of the wheel slip control systems in the art.
Rather than using the aforementioned modulation valve, a wheel slip control system may employ a separate wheel slip control valve that functions in conjunction with the brake equipment. Depending on how the equipment is configured on the vehicle, the slip control valve may be connected to the brake cylinder(s) or brake cylinder supply line(s) on a per axle, per truck or per vehicle basis. The slip control valve on most systems is usually a solenoid valve capable of being commanded to assume any one of several positions. When commanded by the wheel slip controller to a release position, for example, the slip control valve vents pressure from the brake cylinders so as to release the brakes. When commanded to lap position, the valve holds constant whatever pressure is currently in the brake cylinders. When commanded to an apply position, the slip control valve supplies pressure to the brake cylinders so as to reapply the brakes.
The operation of a slip control valve in one type of wheel slip control system is described in U.S. Pat. No. 4,491,920, entitled RATE POLARITY SHIFT WHEEL-SLIP CONTROL SYSTEM. This patent is assigned to the assignee of the present invention, and incorporated by reference into this document. This particular system detects wheel slip by monitoring the rate at which each wheel/axle combination decelerates during braking. A rate determining circuit on each truck determines which wheel/axle combination on the truck exhibits the highest (most negative) rate of deceleration. When the rate of deceleration increases below a first predetermined (negative) threshold, the wheel slip controller commands the slip control valve to the release position thereby reducing the force applied by the brakes to the wheels of truck. This reduction in braking force allows the deceleration rate of the wheel/axle combination to change from being increasingly negative in value to decreasingly negative in value as the axle again approaches the speed of the vehicle. At this point, the rate of the wheel/axle combination, though still negative in value, is now moving positive in direction. The wheel/axle combination is thus accelerating so as to catch up to the speed of the vehicle. When the rate rises above a second predetermined (negative) threshold, the wheel slip controller commands the slip control valve to the lap position thereby maintaining whatever pressure is currently in the brake cylinders of the truck. Once the wheel/axle combination reaches the speed of the vehicle, its rate of change, though positive in value, is now again moving negative in direction because the vehicle has a negative acceleration due to the braking. When the speed of the axle matches that of the vehicle and its rate of change indeed moves in the negative direction, the wheel slip controller commands the slip control valve to the apply position thereby reapplying the brakes to the wheels of truck. Should wheel slip be detected again, the system will again correct it as noted above. It is through such detection and correction that the patented system continually address the problem of wheel slippage.
Many wheel slip control systems work in conjunction mostly with the friction brake control equipment, and merely remove dynamic braking until the wheel slipping problem has been corrected. For example, the slip control valve presented in U.S. Pat. No. 4,491,920, supra, can be commanded to the release, lap and reapply positions accordingly so as to correct the wheel slip that occurs during friction braking. Dynamic braking on the truck, though, may be addressed only to the extent that the propulsion brake controller controlling the AC motors is prevented from electrically braking the axles on the truck while the wheel slip is being corrected. Rail vehicles configured in this manner essentially have their wheel slip control systems alternately apply and release rapidly the friction brakes so that the affected wheel/axle combination experiences an averaged, reduced braking force.
Many other wheel slip control systems correct wheel slip by affecting the operation of both the friction and dynamic braking equipment on the truck. An example of such a wheel slip control system appears in U.S. Pat. No. 5,752,212, entitled PROPORTIONAL POLARITY WHEEL SLIDE PROTECTION. This application is assigned to the assignee of the present invention, and incorporated by reference into this document. This particular system allows the dynamic and friction brake systems to operate basically in harmony while wheel slip is being controlled. It incorporates into the overall brake control system so that the same modulation valve(s) used to modulate the braking force for normal vehicle braking will also be used to modulate the braking force during wheel slip control. Generally stated, this system enables the brake control system to derive a brake command signal through which the dynamic and friction brake equipment each reduce, proportionately, the braking force that each applies to the axles. It does this by taking into account data such as the speed and the acceleration/deceleration rate of the wheel/axle combinations, the severity of the wheel slip and the duration of the wheel slip. This system controls slip whether the vehicle is being decelerated using friction braking or a combination of dynamic and friction braking.
The wheel slip control system described in U.S. Pat. No. 4,941,099, entitled ELECTRONIC ADHESION ADAPTIVE WHEEL SLIDE PROTECTION ARRANGEMENT FUNCTION, is another example of a wheel slip control system that affects the operation of both the friction braking and the dynamic braking equipment on a truck. This patent is assigned to the assignee of the present invention, and incorporated by reference into this document. This particular system uses two detection circuits, a primary wheel slip detection circuit and a synchronous wheel slip detection circuit, each employing its own separate pattern recognition slip control logic. This system combines the separate slip control logic using a relatively complex scheme through which to correct slipping of the wheel/axle combination by modulating the force applied by the brakes to the affected wheel/axle combinations on the truck.
The wheel slip control system described in U.S. Pat. No. 4,941,099 employs detection and correction parameters through which it detects and subsequently corrects slipping of the wheel/axle combinations. Like in other wheel slip control systems in the art, the parameters used by this patented system are stored in memory devices either individually or in the form of tables or both. The detection and correction parameters are constants each of which generally preselected to work with the circumstances of the particular application for which it was intended.
There are many wheel slip control systems that employ such parameters according to principles known in the wheel slip control art. The detection parameters are used by the detection logic embodied in the programming code, whereas the correction parameters are used in the correction logic in the code. For example, as a microprocessor executes the instructions embodied in the programming code, the wheel slip controller monitors various input signals such as rotational speeds and the rates at which the wheel/axle combinations accelerate or decelerate. From these input signals and others, it may derive signals indicative of the vehicle speed, vehicle deceleration and other required information the nature of which depending on the particular wheel slip control system at issue. Based on such signals, the wheel slip controller retrieves the specific detection parameter(s) appropriate to the current operating conditions. Simply stated, the wheel slip controller uses the detection parameters in its detection logic when determining whether any of the wheel/axle combinations are actually experiencing slip. Once wheel slip is detected, the wheel slip controller retrieves the specific correction parameter(s) appropriate to the degree of slip experienced by the affected wheel/axle combination. It is these selected correction parameter(s) that the wheel slip controller uses in its correction logic so that the brake control system may derive a brake command signal through which to correct the slip, i.e., temporarily reduce the braking force applied to the slipping wheel until such slipping ceases or reduces to an acceptable level. The brake command signal or its progeny is sent to the brake control equipment or to the separate wheel slip control valve(s) to correct the slippage.
There are many different types of wheel slip control systems in use today in the rail transport industry and myriad ways in which to incorporate wheel slip control into a brake control system. The type of equipment that any given rail vehicle has and how that equipment may be configured varies from manufacturer to manufacturer and from application to application. For example, wheel slip control systems and brake control equipment have been devised that control braking force on a per axle, a per truck and even a per rail vehicle basis. One disadvantage known in the art is that due to so many equipment configurations there is little or no uniformity in the way in which braking force is controlled to reduce slipping of the wheel/axle combinations.
It is therefore desirable to introduce a measure of uniformity to the wheel slip control art to overcome this disadvantage. As explained in the detailed description section of this document, the present invention may be used to render existing wheel slip control systems capable of being used with brake control equipment whether such equipment is configured to control braking force on a per axle, per truck or per rail vehicle basis. The present invention may be used on rail vehicles whether they feature only friction braking equipment or a combination of friction and dynamic braking equipment. The present invention can achieve this advantage generally through modification of the logic embodied in the programming code executed by the wheel slip controllers/brake control systems on the market. The present invention may also, of course, be incorporated into newly devised systems.
There are other wheel slip control systems that, in whole or in part, relate to the present invention. One such system is described in U.S. Pat. No. 5,471,387, entitled METHOD OF AND APPARATUS FOR THE COMBINED DETECTION OF SPEED VARYING ENERGY LEVEL WHEEL SLIP DETECTION AND DETERMINATION OF WHEEL SLIP INTENSITY OF A RAILWAY VEHICLE BRAKE SYSTEM. Another system particularly relevant to the present invention is described in U.S. Pat. No. 5,654,889, entitled SIMPLIFIED PATTERN RECOGNITION WHEEL SLIDE PROTECTION. These two inventions are assigned to the assignee of the present invention, and are incorporated by reference into this document.
It should be noted that the foregoing background information is provided to assist the reader in understanding the present invention. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.